BIO310: Developmental Biology

Unit 3: CleavageNow that the egg is fertilized, it must still develop from a single
cell into a multicellular organism. The first step in this process is
extremely rapid cleavage; during this time, the egg undergoes a
tremendous amount of cell division without increasing in overall size.
All embryos undergo this stage of development, but different types of
embryos exhibit very different kinds of cleavage patterns.
Also, beginning during cleavage (although this is a process that can
continue during much of development), cells’ fates begin to be
“specified”—that is, they are committed to forming a particular type of
tissue or structure different from other structures. Specification is
the first step in the differentiation process that ends with
determination, at which point cells’ fates are fixed and cannot be
altered based on outside or surrounding influences.

Unit3 Learning Outcomes
Upon successful completion of this unit, students will be able to:

Distinguish between types of cleavage and identify which groups of
organisms undergo which type of cleavage.

Understand the steps of the cleavage process and what effect the
presence or absence of specific molecules and structures have on
that process.

Distinguish between “specification” and “differentiation” and
various types of specification.